objectstore: use types.PathLike

Use the new `types.PathLike`, which is exactly the type that this
module defined too.

osbuild/objectstore.py

@@ -5,8 +5,9 @@ import os
 import subprocess
 import tempfile
 import weakref
-from typing import Optional, Union
+from typing import Optional
 
+from osbuild.util.types import PathLike
 from osbuild.util import ctx, rmrf
 from . import treesum
 
@@ -16,10 +17,6 @@ __all__ = [
 ]
 
 
-# Type for valid inputs to `os.fspath`
-PathLike = Union[str, bytes, os.PathLike]
-
-
 def mount(source, target, bind=True, ro=True, private=True, mode="0755"):
     options = []
     if bind: